A blog commenting on various aspects of the private collecting and trade in archaeological artefacts today and their effect on the archaeological record.

Thursday, 29 October 2015

Two Warsaw Chambers of Numismodeath

This is an attempt to duplicate the results of Dean Crawford's coin-colouring experiment which has been bothering me for a few hours (see my text 'Artefact Hunting, the "Lesser of Two Evils"? More on "Fragmentation"'). I really do not see how the chemistry of what he describes works. On my way back from the shops yesterday I put my hand in my pocket and pulled out a handful of loose change and found that some of the coins were almost straight from the mint. That gave me the idea of trying to duplicate the "kitchen sink experiment" which the metal detectorist used to "prove" to Mr Hooker's readers that artefacts will rapidly self destruct in agricultural soil. Readers of my blog will know that I am sceptical of such generalisations. So, willing to put my money where my mouth is, I decided to put it to the test. I have some fertiliser from my vegetable patch which though it is unbranded, so is Mr Crawfords who just used some random material he found. His is white granules, mine is too. His is good for plants, mine is too. On the label, my fertiliser says it is composed primarily of potassium nitrate, urea and has potassium pentaoxide in it, the latter is nasty stuff - I guess that's why the label says to use gloves (coins beware) it is highly corrosive to metals, maybe we'll get copper phosphate?

All I needed was some dirty dugup coins. Not something I have hanging around at home, but there's a dealer in coins, medals and other such stuff down the road. I got some cruddy ones. I was charged a lot for them when the guy heard I wanted his dirtiest for "an experiment", the moron (coin dealer) thought I was going to "turn them into gold". Hmmm. I then went to get a vessel that could do as "Gloucestershire" and a bucket of earth from a building site where I'd seen some with anthropogenic stuff in it. OK ready.

Experiment 1: Warsaw Chamber of Numismodeath

I made my fertiliser up into a solution as for my garden, 3%. I measured the pH, it is 6.8. A sample of the soil in distilled water tested at 5.6 (this is Mazovia). I assume that Gloucestershire would be more alkaline, but this is what I have. Some soil acids are hostile to buried metals rather than passivating them, and let's give Mr Crawford's idea a chance.

Here is a photo of the ingredients, on a tekkie-style camo jacket (which I happen to have at home) for authenticity. The vessel representing "Gloucestershire" is rather a nice piece of plastic kitsch. It's All Saints Day coming up and in Poland we buy all sorts of crap to decorate the family graves with on that day, so the supermarkets have a variety of these special candle holders... I thought this was quite suitable for the "Warsaw Chamber of Numismodeath" as I called my experiment.

Above I picture the coins, Mr Crawford had four, I thought I'd be more ambitious (besides which having them touch each in wet soil other gives all sorts of potential for electrochemical cells to be set up). There's a wider range here, from mint fresh to dark brown. I degreased them in ethyl alcohol (which I happen to have hanging round the house).

So first I tipped the soil into "Gloucestershire". This took a bit of time as I wanted to make sure there were no worms in there as they'd drown. I thought a depth of seven centimetres would be adequate.

Then I added the coins. Mr Crawford's photo shows his lying on the soil surface. I cannot see how this would work, at the first rainfall, much of the fertiliser would be washed off the upper surface and the lower face would not be wetted. So I decided (to give the chemicals a chance to work) I'd bury some about a centimetre down, and leave some on the surface (see photos). I had a few qualms about one of them, a French frank which was aesthetically worn and patinated, qquite a nice thing. But then, putting my money where my mouth is, my thesis is that coin is not going to come out of my jar looking anything like Mr Crawford's. Let's see.

Then I poured the fertiliser solution all over Gloucestershire - perhaps a little too much as it is currently inundated, but the soil in contact with the coins has taken up the fertiliser with all those nasty compounds that Mr Crawford says will dissolve them into nothing. Soon the water will evaporate and the solution inside will become more concentrated - so bad luck coins, Doomsday is nigh (well, according to Dean Crawford and Baz Thugwit).

Now I intend to keep an eye on the jar, it is on my windowsill (outdoors in November it could well freeze and chemical reactions would stop), I'll keep it moist and then in three weeks (so about the 26th November we'll open it up and see whether my coins look anything like Dean Crawford's and whether that French frank is still in a collectable condition.

Experiment 2: The Warsaw Dungeon of Numismodeath

The second experiment mirrors more closely what Mr Crawford shows in
his photo, where he indicated that he tipped fresh dry fertiliser grains onto dry-looking
earth. There does not seem to be much point trying to duplicate the
colour changes he documents by doing that, moisture surely has to be
present. Again, with winter approaching, in Poland one cannot count on
free moisture in November, so I decided to construct a humidity chamber.

A
plastic sealable food container doubles for Worcestershire. At its base was
placed a dishwasher sponge (which may be assumed for the purposes of the
experiment to be chemically inert) soaked in tap water. On top of this
was laid a 3cm layer of the same soil as used before and dampened
slightly, on top of that were some coins and then a single layer of
granules of artificial fertiliser, on top of which some more coins were
added and then a sprinkling of fertiliser as in Mr Crawford's photo. In order to keep the atmosphere moist, it was decided to use a
second wet (but not saturated) dishwashing sponge separated from the
fertiliser and coin layer with a loose layer 2-3cm thick of plastic
cotton wool buds (again assumed to be chemically inert) with plenty of
air between them. The box was then sealed and we'll take a look in it in
three weeks.

The coins selected fall into two
groups, patinated (5gr 2002 - spotty corrosion breakout, five 2 gr coins
from 1991-2004 and one grosz of 2002) and freshly minted coins of
2014-5 (4x1 grosz, and 3x 5gr). There were no kopieki or other ground-dug coins in this one. As before the coins were degreased
before use.

I decided to buy a more aggressive
fertiliser for this experiment. A trip to the garden centre revealed
that not all manufacturers tell you what is actually in the box, but of
those that did Biopon Autumn grass fertiliser looked to be the nastiest
for buried metals (and by all accounts your skin). It's got all sorts of
stuff in it, Phosphorus pentoxide, potassium oxide, calcium and
magnesium oxide, sulphur trioxide. I reckon if that does not destroy the
coins, not much else will.

UPDATE 3rd November 2015
The flood in Gloucestershire (experiment one) has abated, the coins are now clustering in nicely damp soil, Mr Crawford will be glad to hear that there is already a light green powdery efflorescence on the uppermost edge of one of them, and some interesting minute spots of what looks like redeposited copper where it touches another one below it. I have sealed the top of the vessel off with four layers of polythene and we'll start counting the three weeks for both experiments from today (24th November).

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About Me

British archaeologist living and working in Warsaw, Poland. Since the early 1990s (or even longer) a primary interest has been research on artefact hunting and collecting and the market in portable antiquities in the international context and their effect on the archaeological record.

Abbreviations used in this blog

"coiney" - a term I use for private collector of dug up ancient coins, particularly a member of the Moneta-L forum or the ACCG

"heap-of-artefacts-on-a-table-collecting" the term rather speaks for itself, an accumulation of loose artefacts with no attempt to link each item with documented origins. Most often used to refer to metal detectorists (ice-cream tubs-full) and ancient coin collectors (Roman coins sold in aggregated bulk lots)